I think it would be fitting too if at some point @steemmonsters stops producing legendary cards or significantly lowers the drop rate (from the 4 that it is currently to something like 0.25 or even less), but make it so that you "birth" a new card of the same type once you level it up all the way to max XP.

No matter the rate of gaming events, the amount of XP to be obtained is limited, so the supply coming out of that side ("birthed" cards) should be relatively low, depending on just how much XP can be earned per day on average.

My thought on this is that it adds further incentive to keep playing in the events. The idea that you can double the number of your legendary cards without having to pay a cent more, by simply gaining more and more XP with every event that you play in, should cause the interest in the events to significantly increase, versus not having the added motivation of "increasing position".